Thermal bimetallic relay



Se t. 21, 1965 P. NAUER 3,207,872

THERMAL BIMETALLIC RELAY Filed 00";- 22, 1962 INVENTOR. PAUL NAUER ATTORNEYS United States Patent O 3,207,872 THERMAL BIMETALLIC RELAY Paul N auer, Zug, Switzerland, assignor to Landis & Gyr, AG., Zilg, Switzerland, a body corporate of Switzerland Filed Oct. 22, 1962, Ser. No. 231,931 Claims priority, application Switzerland, Nov. 8,- 1961, 12,942/61 9 Claims. (Cl. 200-88) This invention relates to relay devices and more particularly to thermal relay arrangements.

It is known to amplify small'electric currents or voltages to such an extent that they can satisfactorily actuate higher rated relays having electric contacts adapted for many different purposes such as controlling the operation of servo-motors for actuating electrical controls.

A variety .of constructions are known for such amplifiers including, for example, magnetic amplifiers and sensitive non-voltage relays with large switching relays connected thereto.

Known amplifiers, however, not only have the disadvantage of high production costs but, owing to the larger number of structural parts, to their mechanical sensitivity and other factors, they also have the disadvantage of being sensitive to considerable and varied disturbances.

It is one object of the invention to provide a relay which avoids thesev disadvantages.

This and other objects and advantages of the invention will be set forth in part hereinafter and in part will be obvious herefrom, or maybe learned by practice of the invention, the same being realized and attained by means of the parts, constructions, arrangements, combinations and improvements pointed out in the appended claims.

The invention consists in the novel parts, constructions, arrangements, combinations and improvements herein shown and described.

Two examples of a thermal relay according to the invention are diagrammatically illustrated in the drawing, of which:

FIGURE 1 is a perspective view of a bimetal relay illustratively used with a servo-motor, and having a movably mounted control'element in the form of a heating lug; and

FIGURE 2 is a fragmentary side elevation view of a bimetal relay having a movably mounted control element in the form of a cooling lug.

In FIGURE 1 there is illustrated two contacts 1 and 2 and between them two bimetal strips 3 and 4 which act ascontact carriers and are relatively arranged so that their sides with the greater coefiicient of expansion face outwards. The bimetal strips 3 and'4 are mechanically connected by a transverse member 5 in differential arrangement, so that variations in the ambient temperature have no-eifect on the positions of the strips. The strips are provided with respective contacts 6 and 7'which cooperate alternatively and respectively with the contacts 1 and 2, thus forming two bimetal contact devices. The transversememb'er 5, which connects the bimetal strips approximately at the height of the two contacts 6 and 7, acts also as a spacer ensuring that the distance between the contacts 6 and 7 is always the same, independently of the temperature of the bimetal strips 3 and 4. The contacts 1 and 2 aremounted on normal contact springs 1A, 2A, so that there is frictional contact-making. The two switches formed by the-contacts 1 and 6 and 2 and 7 respectively are located, for example, in the circuit 8 of a servo-motor 9.

Between the two bimetal strips 3 and 4 is a control element embodied in the form of a heating lug 10, which is mounted for movement relatively to the strips in the direction of the arrows. The lug 10 is equipped with a heating coil 11, which receives voltage through supply leads 12and 13 from the terminals 14 of a current source. The leads 12 and 13 are also used as described more fully hereinafter for mounting the heating lug 10.

The movable heating lug 10 is designed and arranged so that'when it is in its central position between the two bimetal strips 3 and 4 it heats both strips to the same temperature. In this position, which is shown in FIGURE 1, the two switches formed by the contacts 1 and 6 and 2 and 8 respectively are open, i.e., the servo-motor 9is deenergized and stationary. However, if the heating lug 10 deviates laterally from its central position to the left or right, such deviation results in unbalanced heating of the bimetal strips 3 and 4 and, depending on the direction in which the heating lug 10 has been moved, the resultant deformation of the bimetal system 3, 4, 5, closes one of the two switches 1, 6 or 2, 7. Thus, the servo-motor 9 is actuated and driven in one or the other direction.

The illustrated embodiment also includes electric measuring means 15 comprising a coil 16, designed as a flat coil, which is mounted between the permanent U-magnets 17, 18 for approximately straight-line movement in the direction of the related arrows. The flat coil 16 is mounted to avoid hysteresis by means of resilient bands 19 and 20, also serving as electric supply leads, and by means of the supply leads 12, 13. The coil 16 is connected, for ex ample, in a Wheatstone bridge circuit 21 containing a measuring member 22, such as a temperature-sensitive resistor, for sensing the measured value. The heating lug 10 is rigidly connected to the flat coil 16by the supply leads 12 and 13, so that it follows the approximately linear deviating movements of the coil.

The apparatus shown in FIGURE 1 operates as follows: The flat coil 16*is acted on by the output voltage of the Wheatstone bridge 21. Thus a force is exerted on the coil 16 which is mounted for linear movement in the magnetic field of the U-magnets 17 and 18. The direction of the force, and thus the direction in which the flat coil 16 moves, depends on the direction of the current output of the bridge. Acting together with the coil 16, the heating lug 10 is moved in one or the other direction between the bimetal strips 3 nd 4. If the lug 10 is moved to the left, for example, towards the bimetal strip 3, this produces a temperature difference between the strips 3 and 4, which causes the bimetal system 3, 4, 5 to deviate to the right towards thecontact 2. Hence, the switch 2, 7 is closed and the controlling servo-motor 9 starts running, for example, clockwise. If on the other hand the heating lug 10 moves to the right, an opposite temperature difference is produced in the bimetal system 3, 4, 5 causing the bimetal system 3, 4, 5" to deviate leftwards towards the contact 1. This makes the switch 1, 6 close and consequently reverses the polarity of the controlling servomotor 9, so that it starts running in'the opposite direction.

The bimetal strips 3 and 4 may also be relatively arranged with their sides-having the greater coeflicient of expansion inwards, i.e., facing one another. The arrangement previously described, with the sides having the greater coefficient of expansion outermost, i.e., 'awlay fromeach other, is particularly favorable, however since, when heating lug 10 deviates, the bimetal strip heated more intensely by it bends towards the lug 10 and is therefore heated to an even greater extent. This accelerates the bending of the bimetal system 3, 4, 5 thus also accelerating the contact movement whereby positive, trouble-free contact-making is effected. Conversely, this arrangementalso'produces favorably accelerated contactopening since, when the heating lug 10 moves back towards the central position, the bimetal strip previouslyheated more intensely simultaneously bends back to regain its original shape, i.e., bends away from the heating Patented Sept. 21, 1965- 3 lug 10, so that the bimetal system 3, 4, 5 and thus the movable contact, moves out of its closed position with increasing velocity away from the fixed opposite contact.

FIGURE 2 illustrates in part another construction of the bimetal relay. A non-heated cooling lug 23 is arranged as a movably mounted control element between two heated bimetal strips 24 and 25 which are mechanical-1y connected for differential action by a transverse member 5. The cooling lug 23 is actuated by a measuring element (not shown) for example, by the arrangement of FIGURE 1, and can be displaced by this element in the directions of the two arrows. The inwardly directed sides 26 and 27 of the bimetal strips 24 and 25 have the greater coeflicient of expansion.

Contacts 28, 29 and 30, 31, together with the two bimetal strips 4 and 25, form two bimetal contact devices like those in the FIGURE 1 construction.

When the cooling lug 23 is in its central position between the two bimetal strips 24 and 25 it absorbs equal amounts of heat from them, so that the two strips 24 and 25 which were heated to the same temperature are now subjected to equal cooling. The strips 24 and 25 are then in their initial shape shown in FIGURE 2, i.e., they are not curved, and the two switches 28, 29 and 30, 31 are open.

If the cooling lug 23 moves, for example, to the right towards the bimetal strip 25, the latter is cooled more intensely than the bimetal strip 24. This makes the bimetal system 24, 5, 25, curve to the right towards the contact 31, and the switch formed by the contacts 30, 31 is closed. If on the other hand the cooling lug 23 bends to the left towards the bimetal strip 24, then the bimetal system 24, 5, 25, bends in the opposite direction, and the switch 28, 29 is closed.

The bimetal strips 24 and 25 can also be relatively arranged so that their sides 26 and 27 having the greater coefficient of expansion are on the outside, i.e., away from one another. The arrangement shown in FIGURE 2, however, with the sides 26 and 27 having the greater coefficient of expansion inside, i.e., facing one another, is particularly favorable in the present case since, when the cooling lug 23 is deflected, the bimetal strip cooled more intensely by it bends towards the lug 23 and is therefore cooled to an even greater extent with the result that the bending-out movement of the bimetal system 24, 5, 25, is accelerated. Hence, the related contact movement is also accelerated, i.e., there is positive trouble-free contact-making effected. Conversely, this arrangement also produces favorably accelerated contact-opening since, when the cooling lug 23 moves back towards the central position, the bimetal strip previously cooled more intensely simultaneously bends back to regain its original shape, i.e. bends away from the cooling lug 23, so that the bimetal system 24, 5, 25, and thus the movable contact, moves out of its closed position with increasing velocity away from the fixed opposite contact.

Thus, when the control element is in the form of a cooling lug the closing and opening characteristic of the switches is particularly favorable if the sides of the bimetal strips having the greater coefficient of expansion are arranged facing one another, whereas for the same physical reasons, when the control element is in the form of a heating lug, the switching characteristic is particularly favorable if the sides of the bimetal strips having the greater coefficient of expansion are arranged away from one another.

Other structural embodiments of the bimetal relay are also possible. For example, the control element mounted for movement relative to the bimetal strips can be in the form of two heating lugs arranged outside the bimetal system to the left and right of the bimetal strips and mechanically. connected together. In this case the measuring element moves the heating system, one heating lug moving towards one bimetal strip while the other heating lug simultaneously moves away from the other bimetal strip. A movably mounted control element made up of two mechanically connected cooling lugs could similarly be used. Instead of using two bimetal contact devices several such devices or only one can be provided, and instead of a servo-motor other appliances may be controlled. The bimetal relay describe-d may be affected not only by the measured value but also by a return or follow-up (feedback) mechanism.

The bimetal relay of the constructions described can also be advantageously used with other measuring elements. The measuring element may, for example, take the form of a rotary coil instrument, the coil being mounted for rotation against a resilient returning force in the magnetic field of a permanent magnet. Instead of one winding the coil of the measuring element may have a plurality of windings for the purpose of adding and subtracting electrical values.

A lever transmission may also be providedbetween' the meaasuring element and the control element mounted for movement relative to the bimetal strips, to increase the extent and velocity of the deviating movement of the measuring element as it is transferred to the control element. The lever transmission, which can be realized particularly easily when a rotary coil instrument is used as a measuring element by applying the principle of the one-armed lever, increases the sensitivity of the bimetal relay.

Any other permanently dynamic system, for example with a plunger, can be used as control member, as can electro-dynamic and mechanical systems, such as hygrometers, or thermal systems.

The bimetal relay according to the invention has the advantage that with it strong contacts can be simply, cheaply and reliably operated with substantial contact pressure from small measured values. It is distinctive in that the initial value need move only a small, light control element which is mounted almost without friction and has a very low mass moment of inertia, and which thus requires only very small activating forces. The necessary contact pressure is produced by the bimetal strips, so that. the system according to the invention acts to a certain extent like a simple servo-system," where only very small forces need be applied to the control element, for example about 0.1 g, and where a contact force many times larger, for example about 10 g, is nevertheless obtained With frictional contact-making.

The invention in its broader aspects is not limited to the specific mechanisms shown and described but departures may be made therefrom within the-scope of the accompanying claims without departing from the prin-. ciples of the invention and without sacrificing its chief advantages.

What is claimed is:

1. A thermal relay for providing an output indication related to an applied electrical signal, comprising a set of electrical contacts, temperature responsive means for operating said contacts and thereby provide said output indication; electromechanical means operatively connectable for response to said applied electrical signal; and a thermal control member in proximity with said temperature responsive means and mounted for movement toward and away from said temperature responsive means, said control member being so coupled to said electromecham ical means that the position thereof is a function of said applied electrical signal; said thermal control member being operative to provide a temperature differential so that said contacts are operated in accordance with the position of said control member relative to said temperature responsive means.

2. A thermal relay in accordance with claim 1 wherein said temperature responsive means is a bimetallic contact member, and said thermal control member includes a heating element.

3. A thermal relay in accordance with claim 1 wherein S d temperature responsive means is a heated bimetal lic contact member and said thermal control member includes a thermally conductive cooling member.

4. A thermal relay for providing an output indication related to an applied electrical signal comprising bimetallic contact means adapted to provide said output indication; means for providing a magnetic field; an electromagnetic moving coil means disposed in said magnetic field and operatively connectable for energization by said applied electrical signal; and thermal control means coupled to said moving coil means and mounted for movement toward and away from said bimetallic contact means, said thermal control means being operative to affect the temperature of said bimetallic contact means in accordance with the position relative thereto to thereby control said output indication.

5. A thermal relay for providing an output indication related to an applied electrical signal comprising contact means including a pair of spaced-apart bimetallic elements; a control member mounted for lateral movement between said bimetallic elements; electromechanical means operatively coupled to control the position of said control member as a function of said applied input signal; and thermal means coupled to said control member and operative to alfect the temperature of said bimetallic elements in accordance with the position of said control member.

6. A thermal relay in accordance with claim 5 wherein said thermal means is an electrical heating element.

7. A thermal relay in accordance with claim 6 wherein each of said bimetallic elements includes a pair of metallic members having diiferent coefficients of expansion and wherein said metallic members having the greater coefficients of expansion face outwardly away from said movable heating element.

8. A thermal relay in accordance with claim 5 wherein said thermal means is a cooling element.

9. A thermal relay in accordance with claim 8 wherein each of said bimetallic elements includes a pair of metallic members having difierent coefficients of expansion and wherein said metallic members having the greater coefficients of expansion face inwardly toward said movable cooling element.

References Cited by the Examiner UNITED STATES PATENTS 2,225,975 12/40 Bruce 200122 X 3,064,103 11/62 Biermann et al 200122 References Cited by the Examiner UNITED STATES PATENTS 2,195,947 4/40 Uhln'g. 2,744,178 5/56 Eckberg. 2,836,366 5/ 5 8 Eckberg.

FOREIGN PATENTS 409,605 5 48 Canada. 448,355 5/ 48 Canada. 485,713 8/52 Canada. 555,058 12/57 Canada. 1,109,484 l/56 France.

621,639 11/35 Germany. 730,547 1/ 43 Germany. 856,370 11/52 Germany. 1,077,446 3/60 Germany.

BERNARD A. GILHEANY, Primary Examiner. 

1. A THERMAL RELAY FOR PROVIDING AN OUTPUT INDICATION RELATED TO AN APPLIED ELECTRICAL SIGNAL, COMPRISING A SET OF ELECTRICAL CONTACTS, TEMPERATURE RESPONSIVE MEANS FOR OPERATING SAID CONTACTS AND THEREBY PROVIDE SAID OUTPUT INDICATION; ELECTROMECHANICAL MEANS OPERATIVELY CONNECTABLE FOR RESPONSE TO SAID APPLIED ELECTRICAL SIGNAL; AND A THERMAL CONTROL MEMBER IN PROXIMITY WITH SAID TEPERATURE RESPONSIVE MEANS AND MOUNTED FOR MOVEMENT TOWARD AND AWAY FROM SAID TEMPERATURE RESPONSIVE MEANS, SAID CONTROL MEMBER BEING SO COUPLED TO SAID ELECTROMECHANICAL MEANS THAT THE POSITION THEREOF IS A FUNCTION OF SAID APPLIED ELECTRICAL SIGNAL; SAID THERMAL CONTROL MEMBER 